In the GNU C Library (glibc) from version 2.17 onwards, the crypt()
function call can return NULL when the salt violates specifications or
the system is in FIPS-140 mode and a DES or MD5 hashed password is
passed. When Cyrus-SASL’s authentication mechanisms call crypt(), a
NULL may be returned.

Impact

A remote attacker could trigger this vulnerability to cause a Denial of
Service condition.